Increased interest in long distance bicycling and bicycling over rugged terrain have brought about several attempts to reduce the rigors of such bicycling by providing a suspension system integral to the bicycle frame. A fundamental problem of providing significant additional comfort via a suspension system, is the addition of significant additional weight and the loss of efficiency. Additional weight is undesirable in the context of human-powered vehicles.
Lawwill U.S. Pat. No. 4,789,174 illustrates a bicycle having a suspension system which comprises an elaborate multi-pivoted interconnection of swing arms, control arms and hub plates configured in a trapezoidal arrangement and connected to a bicycle seat riser tube. The multi-pivoted trapezoidal configuration facilitates the application of balanced forces to the rear wheel from the chain during pedaling. A shock absorber connected to the swing arms in the trapezoidal configuration absorbs shocks during riding. The Lawwill suspension system however, because of the elaborate trapezoidal arrangement and the numerous pivot points and associated hardware required for implementation, adds significant weight to the bicycle frame.
A bicycle rear wheel suspension system having a shock absorber mounted coaxially inside a top frame tube is disclosed in Shuler U.S. Pat. No. 4,679,811. The shock absorber is anchored at one end to a double pivoted swing arm rear wheel mount. On-demand mode selection provides selection of a rigid/nonsuspension rear wheel or a spring/suspension rear wheel by means of a remote actuated cylinder disposed inside the shock absorber. The double pivot and the actuated cylinder mode selectable shock absorber, add significant undesirable weight in this implementation.
Other bicycle frame suspension systems incorporating shock absorbers are known in the art, such as the frame illustrated in FIG. 1. Such a frame avoids the elaborate configurations taught in Lawwill and Shuler, and the associated additional weight. The frame of FIG. 1 is typically made from tubing of aluminum or chromium molybdenum steel alloy, for light weight, and has a triangular configuration 10 comprising an elevated chainstay 12 pivotably mounted to the seat riser tube 14. The triangular configuration 10 is further connected to the seat riser tube 14 by a shock absorber 16. Such a configuration relies on a pivot 18 and the resiliency of the shock absorber 16, to provide suitable suspension and to maximize energy transfer, by the chain, to the rear wheel during pedaling. This prior art configuration, although implemented in lightweight tubing for weight considerations, has the integral pivot 18 which must be big and heavy to withstand the significant forces exerted upon it. Such a pivot adds considerable complexity to frame construction, has negligible resiliency to aid in shock absorbtion and also adds significant additional weight. Further, because the triangular member pivots freely, but for the constraint of the shock absorber, the shock absorber alone facilitates the resiliency of the triangular member. As the shock absorber is the only resilient component in this suspension system, it is required to be larger and heavier to withstand extended use.